1. Field of the Invention
The present invention relates to a propylene-ethylene block copolymer in which ethylene-propylene copolymer segments of a uniform rubber-like elastomer component are dispersed in the matrix of propylene homopolymer segments having high stereospecificity. Precisely, the invention relates to a propylene-ethylene block copolymer which is characterized in that ethylene-propylene copolymer segments of not a mixture of plural rubber-like elastomers each having a different degree of hardness but a uniform rubber-like elastomer component are dispersed in the matrix of propylene homopolymer segments of that type.
The invention also relates to a propylene-ethylene block copolymer in which copolymer segments having a large proportion of ethylene-propylene copolymer fragments are dispersed in the matrix of propylene homopolymer segments having high stereospecificity. Precisely, the invention relates to a propylene-ethylene block copolymer which is characterized in that copolymer segments having a small proportion of crystalline polyethylene fragments relative to the ethylene content thereof and therefore having a large proportion of ethylene-propylene copolymer fragments relative to the same are dispersed in the matrix of propylene homopolymer segments of that type.
2. Description of the Related Art
Various studies for improving propylene-ethylene block copolymers have heretofore been made, which are specifically directed to the improvement in the physical balance of rigidity and impact resistance of the copolymers. One good approach thereto is to investigate the copolymers from the aspect of their solid structure morphology. Briefly, propylene-ethylene block copolymers are composed of propylene homopolymer segments that constitute the matrix of the copolymers and ethylene-propylene copolymer segments of a rubber-like elastomer dispersed in the matrix. To improve their properties, the influence of the solid structure of the copolymers on the strength characteristic thereof is first analyzed for various factors of the copolymers, including the proportion of the constituent segments thereof, and also the molecular weight and the stereospecificity of each constituent segment, and thereafter the thus-analyzed data are reflected on polymer designing and are further fed back to the technique of producing the intended polymers.
As a result of various studies to that effect, it has be en clarified that, in propylene-ethylene copolymers, the molecular weight of the ethylene-propylene copolymer segments constituting the rubber-like elastomer component has governing influences on the physical balance of rigidity and impact resistance of the copolymers.
In that situation, however, it is further desired to develop propylene-ethylene block copolymers having more improved impact resistance.